A Group of Pictures is a concept for video compression. Each one is:
a full frame (AKA "keyframe" or "I-frame") (kinda like a JPEG, etc.) of a video
followed by partial frames (AKA "P-frames" and "B-frames")
(imagine a bunch of smaller tiles that contain parts of the video for
the changing areas).
Nearly all video compression codecs are the same like that.
Usually, they span about 1/10th of a second to 2 seconds (but that varies, depending
on codec, complexity of scene, movement of scene, bitrate, etc.)
So what I've done is converted my 2007 video to MPEG-TS (the same format your TV knows and loves),
and swapped every pair of GOPs here. Each GOP has timing information, so due to my
swapping, we get a nice additional effect where the outputted version "stalls" waiting for frames to
"fill in" the "empty time slots" (if you will), which never come (because they came before).
So we get this *additional* neat effect of "stalling" the end of the 2nd GOP in each pair.
Ergo, I get to turn video compression on itself. 8-)